FIGS. 1A and 1B illustrate a configuration of an optical module described in Japanese Patent Application Laid Open No. 2005-165125 (published on Jun. 23, 2005), which is an example of conventional optical modules. The optical module in the example includes a lead frame 11, a light-receiving device 12, a sealing structure 13, a ferrule 14, a preamplifier 15 and a capacitor 16.
The lead frame 11 includes a plurality of terminals 11a to 11e. The terminal 11a is a terminal for supplying power to the light-receiving device 12 and includes a light-receiving device mounting area 11f. Electrodes are formed on two opposed surfaces of the light-receiving device 12. Mounting the light-receiving device 12 on the light-receiving device mounting area 11f electrically connects one of the two electrodes of the light-receiving device 12 to the terminal 11a. 
An opening 11g is formed in the light-receiving device mounting area 11f. Light from an optical fiber 17 held by the ferrule 14 is guided to the light receiving surface 12a of the light-receiving device 12 through the opening 11g. 
The terminal 11b is a GND terminal and includes a preamplifier mounting area 11h. The preamplifier 15 and the capacitor 16 are mounted in the preamplifier mounting area 11h. The preamplifier 15 is electrically connected to the other electrode of the light-receiving device 12 through a bonding wire. The capacitor 16 is a parallel plate capacitor. The preamplifier 15 is connected to the terminal 11c, which is a power supply terminal, through the capacitor 16.
The terminals 11d and 11e are terminals for outputting signals from the preamplifier 15 and are electrically connected to the preamplifier 15 through bonding wires.
The lead frame 11 is covered with the sealing structure 13 in such a way that one end of each of the terminals 11a to 11e is exposed. The sealing structure 13 is molded of a resin that is transparent to light from the optical fiber 17 and includes a positioning part 13a, a light path conversion part 13b and a device placement part 13c. 
The positioning part 13a includes a ferrule enclosing part 13d and an optical fiber enclosing part 13e. The ferrule enclosing part 13d defines the position of the ferrule 14 and the optical fiber enclosing part 13e defines the position of the optical fiber 17.
The light path conversion part 13b includes an incidence surface 13f and reflective surface 13g. The reflective surface 13g reflects light exiting the optical fiber 17 and transmitted through the incidence surface 13f to allow the light to be incident on a light receiving surface 12a. 
The device placement part 13c is a part for exposing the light-receiving device mounting area 11f and the preamplifier mounting area 11h of the lead frame 11 and is recessed. The device placement part 13c is ultimately covered with a potting resin, which protects the light-receiving device 12, the preamplifier 15, the capacitor 16 and the bonding wires.
In the optical module described above, the light-receiving device has a configuration in which electrodes are provided on two opposed surfaces, one of the electrodes is mounted on and connected to a lead frame and the other electrode is connected by wire bonding. However, light-receiving devices and light emitting devices are not limited to ones that have this electrode arrangement. For example, some types of light-receiving devices and light emitting devices are flip-chip bonded. In a flip-chip bonded surface emitting device or surface light-receiving device, multiple electrodes are disposed on the surface where light emitting surface or light receiving surface are located.
The electrodes arranged in this way are tiny and the lead frames to which they are flip-chip bonded also need to be miniaturized accordingly.
A flip-chip bonding method that applies ultrasonic vibration to a chip (device) for bonding is also used. In this method, lead frames need to be firmly fixed to ensure that ultrasonic vibration is precisely applied to a portion to be bonded.
However, as seen in the fixing structure of the light-receiving device mounting area 11f of the lead frame 11 of the optical module illustrated in FIGS. 1A and 1B, the light-receiving device mounting area 11f is merely placed on the sealing structure 13 and only the bottom surface is in contact with the sealing structure 13. Therefore, the lead frame 11 is not firmly fixed on the sealing structure 13 and it is highly possible that ultrasonic vibration applied will vibrate the lead frame itself. If the lead frame is miniaturized according to the sizes of the electrodes of the surface emitting device or the surface light-receiving device to be flip-chip bonded, the possibility of lead frame vibrating may so increase that enough bonding strength cannot be achieved and problems such as bounding failures may result.